Measurement of the temperature dependence of the Buckingham effect (electric-field-gradient-induced birefringence) in gases

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Abstract

The aim of this research project was to assemble an apparatus to measure the
electric quadrupole moments of gas molecules using the technique of electricfield-
gradient-induced birefringence, or the Buckingham effect. Comprehensive
research by various workers in the field has shown that this technique
provides the only direct means of obtaining the quadrupole moment of a
molecule.
Theory has shown that the most accurate determination of the electric quadrupole
moment is through a study of the temperature dependence of the effect. This
not only allows for the quadrupole moment to be obtained but also enables
the temperature-independent quadrupole hyperpolarisability term to be extracted.
Both the quadrupole moment and the hyperpolarisabilty provide
valuable information in a variety of applications, including intermolecular
forces, electrostatic potentials and non-linear optical phenomena.
This thesis fully describes the apparatus used in these measurements, including a description of the custom built oven that allowed for measurements
to be performed over a temperature range spanning from 25"C up to
200"C. Results for the quadrupole moments and quadrupole hyperpolarisabilities
of carbon dioxide, carbon monoxide, nitrous oxide and hydrogen are
presented, together with a quadrupole moment for carbonyl sulphide from
room-temperature measurements. Wherever possible, the results of this work
are compared to previously published experimental and theoretical data.